The number of salmon returning from the ocean to Norway each year is now less than half of the level in the 1980s. Still, the number of salmon spawning in the rivers has increased.
The abundance of wild Atlantic salmon (Salmo salar) has declined. The number of salmon returning from the ocean to Norway each year is now less than half of the level in the 1980s. Still, the number of salmon spawning in the rivers has increased. The increased number of spawners despite reduced numbers returning from the ocean is due to reduced fisheries in the sea and rivers. Reduced exploitation has more than compensated for the decline.
The reasons for the decline of Atlantic salmon are impacts of human activities in combination with a large-scale decline in the sea survival. The largest declines are seen in western and middle Norway, and negative impacts of salmon farming have contributed to this. Declines due to salmon lice induced mortality will make it difficult to continue sustainable fisheries, particularly in parts of western Norway.
Escaped farmed salmon, salmon lice and infections related to salmon farming are the greatest anthropogenic threats to Norwegian wild salmon. The present level of mitigation measures is too low to stabilize and reduce these threats.
Hydropower production, other habitat alterations and introduced pink salmon (Oncorhynchus gorbuscha) are also major threats to wild salmon. Hydropower production and other habitat alterations significantly reduce salmon populations, and there is large potential for further mitigation measures. Pink salmon is a new threat, and there is need for national and international measures to reduce the risk of negative impacts on native salmonids, including Atlantic salmon.
Due to liming of rivers and reduced emissions, the risk of increased negative impacts due to acid rain is small. Salmon populations in southern Norway have increased due to comprehensive liming programs, which have improved the water quality in rivers affected by acid rain.
Successful efforts to reduce the impacts of acid rain and the introduced parasite Gyrodactylus salaris have increased salmon populations in impacted regions. Overfishing is almost eliminated due to fishing regulations reducing exploitation.
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